Dan28, The confusion is "Cannondale" .. Not reallyCannondale did their own 1&1/2" headset originally to fit the suspension in the steerer, aka headshok.
It's slightly different to the later 1.5" headset - stack height, insertion and bearings.
Additionally, I think the cannondale is actually 1.56, but believe it's adaptable if you're careful.
Fork length might be a challenge.
A True Dalester should pop up and clarify if we are lucky
PM meDoes anyone have or know where I can get headset reducer cups to take a 11/4” headtube down to 11/8” in order to use a 11/8” headset and forks
Thanks